The small GTPase KlRho5 responds to oxidative stress and affects cytokinesis.

Abstract

Rho5 is the yeast homolog of the human small GTPase Rac1. We characterized the genes encoding Rho5 and the subunits of its dimeric activating GEF, Dck1 and Lmo1, in the yeast Kluyveromyces lactis. Rapid translocation of the three GFP-tagged components to mitochondria upon oxidative stress and carbon starvation indicate a similar function of KlRho5 in energy metabolism and mitochondrial dynamics as described for its Saccharomyces cerevisiae homolog. Accordingly, Klrho5 deletions are hyper-resistant towards hydrogen peroxide. Moreover, synthetic lethalities of rho5 deletions with key components in nutrient sensing, such as sch9 and gpr1, are not conserved in K. lactis. Instead, Klrho5 deletions display morphological defects with strengthened lateral cell walls and protruding bud scars. The latter result from aberrant cytokinesis as observed by following the budding process in vivo and by transmission electron micrographs of the bud neck region. This phenotype can be suppressed by KlCDC42G12V encoding a hyper-active variant. Data from live-cell fluorescence microscopy support the notion that KlRho5 interferes with the actin moiety of the contractile actomyosin ring, with consequences different from those previously reported for mutants lacking myosin.